Is the float absorbing fuel and getting heavy? That would be my first guess... especially if you have already readjusted it once, and it continues to be start running rich over time..
I replaced the plastic-foam float in my 1945 with brass.. NOT sure that such is a good practice, as it was difficult to get the float level adjusted correctly, as the brass ones do not float quite as high on the fuel level... Still not sure i have it correct!!! But they do solve the fact that the foam ones can absorb fuel over time..
